Field of the Invention
The present invention relates in general to a drillstring combination pressure reducing and signaling valve assembly. More particularly, the invention relates to the pressure reducing and signaling valve assembly having multiple ball valves of different bore sizes used to meter the flow through the drillstring.
Description of the Related Art
Historically, petroleum drilling in deep waters has been plagued by the effects of the differential density between the downwardly flowing and returning mud columns and sea water over the depth of the sea at the well site. This differential density results in a relatively large pressure differential between the mud column and sea water at the sea bed. This large pressure differential affects not only the well casing settings required, but it may even result in an inability to reach the target depth of the well.
Various remedies for this problem have been suggested, and early trials of some approaches have been made. In one system, the returns from the well are pumped to the drilling rig at the ocean surface by a pumping arrangement close to the seabed. However, none of the current approaches have provided the needed solution to the pressure differential at the seabed caused between the down flowing mud column and the sea water.
Solutions such as using a pressure reducing valve in the drillstring have not been successfully achieved due to the abrasive nature of drilling fluids and the very high velocities of the drilling fluid. Furthermore, positioning a pressure reducing valve intermediate to the length of a drillstring would effectively negate the use of mud pulse telemetry equipment in marine drilling, as the pressure reducing valve would block the relay of pressure pulse telemetry signals from both above and below the valve.
A need exists for a pressure reduction device for use in an intermediate position in a drillstring which provides a long service life and provides a means for overcoming the blockage of mud pulse telemetry through the drillstring.